Coverage Mapper is a crowd sourced cellular signal strength mapping application. The Coverage Mapper application runs on your mobile device (currently only available for Android), collects signal strength data, tied to your location, and submits it to our server. With the data from many people, accurate coverage maps are generated, to give you a better idea of the coverage in areas you care about.
Coverage Mapper is a work in progress for CDMA-based networks, but it is working great for GSM-based networks. You can find the Android application in the Android Market. Please report any issues on the forum.